How can I improve my Spam Complaint Level (SCL) on Outlook?
Michael Ko
Co-founder & CEO, Suped
Published 3 May 2025
Updated 19 Aug 2025
9 min read
Improving your Spam Confidence Level (SCL) on Outlook is crucial for email deliverability. Microsoft 365 and Outlook.com use SCL as a key indicator to determine if an email is spam, assigning scores from 0 (least likely to be spam) to 9 (most likely). A higher SCL score means your emails are more likely to land in the junk folder, or even be rejected.
Many email marketers experience a common challenge: transactional emails, like double opt-in confirmations, might land in the inbox with a low SCL, but subsequent marketing emails end up in junk. This often points to a difference in how these email types are perceived, even if they originate from the same sending infrastructure. We need to look beyond just the technical setup and delve into sender reputation and content quality.
Understanding what factors influence your SCL is the first step. It's not just about technical configurations, but also about recipient engagement, content relevance, and list hygiene. Let's explore the strategies to help you achieve a lower SCL and ensure your emails reach the inbox.
Verify your email authentication
Email authentication is foundational to establishing trust with email providers, especially Microsoft's systems. Properly configured Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM), and Domain-based Message Authentication, Reporting, and Conformance (DMARC) records signal to Outlook that your emails are legitimate and haven't been tampered with. This significantly reduces the likelihood of your emails being flagged as suspicious and receiving a high SCL.
An incorrectly configured DMARC record, or a lack of one, can heavily impact your sender reputation and, consequently, your SCL. It is essential to ensure that your authentication protocols are not only present but also correctly aligned with your sending practices. Even if your emails technically pass authentication, issues like a misconfigured DMARC can still lead to deliverability problems.
SPF setup: Ensure your SPF record includes all authorized sending IP addresses and domains. Microsoft systems specifically check this.
DKIM signing: Make sure your emails are properly signed with DKIM. This provides cryptographic verification of the sender's identity.
DMARC policy: Implement a DMARC policy, even if it starts with p=none, to gain visibility into your email ecosystem. Gradually move to p=quarantine or p=reject as your configuration becomes stable. For more information, see our guide on DMARC, SPF, and DKIM.
Regularly check your authentication records for errors or misconfigurations. Even small changes to your email infrastructure can impact these records, leading to authentication failures and higher SCL scores.
Focus on sender reputation and engagement
Your sender reputation is arguably the most significant factor influencing your SCL. If recipients consistently mark your emails as spam, or if you have a high bounce rate, your reputation will suffer, leading to higher SCL scores. Microsoft's systems, including Microsoft Defender for Office 365, heavily rely on reputation to filter mail.
Engagement plays a critical role here. If users consistently open, click, and reply to your emails, it sends positive signals to Outlook. Conversely, low open rates, high delete rates, or a significant number of spam complaints will increase your SCL. This is why automated transactional emails, which typically have high engagement, often see better inbox placement than marketing emails.
Minimize spam complaints: Provide a clear and easy unsubscribe link in every email. Monitor feedback loops (FBLs) and immediately remove users who report your emails as spam. This directly impacts your Bulk Complaint Level (BCL) and, in turn, your SCL.
Maintain list hygiene: Regularly clean your email lists by removing inactive subscribers, invalid addresses, and known spam traps. Sending to unengaged or invalid addresses hurts your reputation. Refer to our article on spam traps to learn more.
Encourage engagement: Send relevant and valuable content. Personalize your emails and segment your audience to ensure your messages resonate with recipients.
The content of your emails also plays a significant role in determining your SCL. Certain elements can trigger spam filters, even if your sender reputation is good. Outlook's filters analyze various aspects, from text and images to links and HTML structure.
Avoid spam trigger words: Words or phrases commonly associated with spam (e.g., 'free money,' 'guarantee success') should be minimized. While not as impactful as reputation, they can contribute to a higher SCL.
Optimize formatting: Excessive use of exclamation points, all caps, or unusual fonts can appear suspicious. Ensure your HTML is clean and well-structured, and that the text-to-image ratio is balanced. Large images or many links can increase your SCL if not managed properly. You can find more details in our guide on improving deliverability for large emails.
Be mindful of links: Ensure all links are legitimate and lead to trusted domains. Redirects or suspicious-looking URLs can significantly raise your SCL.
Consider your audience and tailor your content to their expectations. Generic, untargeted content is more likely to be marked as spam, even if it doesn't contain obvious spam triggers. The perceived relevance of your email directly impacts how recipients interact with it, which then feeds back into your SCL.
Monitor and diagnose deliverability issues
Understanding how Outlook processes emails is key to proactively managing your SCL. Microsoft utilizes several layers of filtering, including SCL and Bulk Complaint Level (BCL), to assess incoming messages. For more detail on these ratings, see our article on what are Microsoft SCL and BCL ratings.
Regularly monitoring your email performance can provide early warnings of SCL issues. If you notice a sudden drop in inbox placement rates for Outlook recipients, it's time to investigate your email headers for SCL scores and review your sending practices. Microsoft also has policies for anti-spam that can be configured for cloud mailboxes to better manage these scores.
For specific diagnostics, analyze the email headers of messages that land in junk. Look for the X-Forefront-Antispam-Report header, which contains the SCL, BCL, and other relevant scores. This information can help pinpoint the exact reason for the higher SCL. For example, if you see an SCL of 5 or 6, it indicates the message was marked as spam by the content filter. If you're experiencing persistent issues, our article on fixing Outlook junk mail placement might offer further assistance.
Another area to inspect is whether your domain or sending IP address is on any blocklist (or blacklist). While not directly an SCL factor, being listed can severely impact deliverability and indirectly contribute to higher SCLs because blocklists are a strong signal of poor sending practices. Regularly check if your domain or IP is listed on any major blocklist using a blocklist checker.
Optimize list management and subscriber engagement
Outlook places a strong emphasis on recipient engagement and the quality of your mailing list. If your list contains a high percentage of inactive or disengaged users, or if you acquire contacts without proper consent, it can lead to elevated SCLs and poor deliverability.
Implement double opt-in: This is a crucial step to ensure that every subscriber genuinely wants to receive your emails. As seen with the Klaviyo example, confirmed opt-in emails often achieve better inbox placement due to higher initial engagement and lower complaint rates.
Segment your audience: Send targeted content based on user preferences and behavior. This increases relevance and engagement, naturally reducing spam complaints. For newsletters, specific strategies can further improve this. Learn more about improving deliverability for newsletters.
Manage inactive subscribers: Implement a re-engagement strategy for inactive subscribers. If they remain unengaged, consider removing them from your active mailing list to protect your sender reputation. Sending to unengaged contacts can increase your SCL.
By actively managing your subscriber list and focusing on sending emails to genuinely interested recipients, you can significantly lower your spam complaint rates and improve your SCL on Outlook.
The path to better deliverability
Improving your SCL on Outlook is a continuous process that involves a combination of technical best practices and strategic content delivery. By prioritizing email authentication, nurturing a strong sender reputation through engagement, and carefully crafting your email content, you can significantly reduce your SCL and achieve better inbox placement for all your campaigns. Regularly monitoring your performance and adapting your strategies based on feedback will be key to long-term success.
Views from the trenches
Best practices
Always use confirmed opt-in for new subscribers to ensure high engagement and minimize complaints.
Regularly monitor Microsoft's feedback loop (FBL) and Junk Mail Reporting (JMR) program to identify and remove complainers promptly.
Segment your audience and personalize content to meet recipient expectations, increasing engagement rates.
Maintain a clean email list by removing inactive subscribers and hard bounces.
Ensure all email authentication (SPF, DKIM, DMARC) is correctly configured and aligned.
Common pitfalls
Sending to non-opt-in lists or purchased lists, leading to high spam complaint rates.
Ignoring feedback loop data, which means continuing to send to users who marked your email as spam.
Sending too frequently or irrelevant content, causing recipient fatigue and complaints.
Having unoptimized email content with too many links, images, or spammy keywords.
Not having a DMARC record or having one that is misconfigured, hurting domain reputation.
Expert tips
If transactional emails have a low SCL but marketing emails have a high SCL, examine content, frequency, and audience targeting for the marketing sends.
A low SCL for double opt-in emails and a high SCL for marketing emails indicates a recipient engagement issue with your marketing content.
Check for any issues where links in your emails might be seen as malicious or unwanted.
Focus on the 'why' behind the SCL difference: recipients are explicitly telling Microsoft they don't want your marketing messages.
Ensure your sending infrastructure is consistent between transactional and marketing emails to rule out technical setup as the primary cause.
Marketer view
Marketer from Email Geeks says to send only to people who have actively opted in so that recipients do not mark your mail as spam because they do not want it. This implies that forgetting to uncheck a box is not actively opting in.
2022-11-18 - Email Geeks
Marketer view
Marketer from Email Geeks says to make sure the links in your message are not being sent to people who do not want it through other channels.
